If you installed with the DSL HDD-Install script and GRUB, then you should have the option on startup to boot in "runlevel 2" which doesn't start X. If you set up the bootloader yourself, just create another listing of DSL with "2" at the end of the "kernel" line. Note that you won't be able to run X properly in runlevel 2 using the "startx" command.

There is more info about boot cheatcodes on the Wiki (http://www.damnsmalllinux.org/wiki/cheat_codes.html).

I haven't used LILO, so I don't know much about it. However couldn't you simply boot to a DSL CD and change the settings back with that?

Anyhow, perhaps you can comment out the line in "/home/dsl/.xserverrc" to stop X loading on startup. That might break the "startx" command though, so you might need to specify all the options to start X on the comand line (or make your own script), look at the startx man page (http://www.xfree86.org/4.2.0/startx.1.html). I don't know if that will work, but there are probably more elegant ways if you look into the scripts of DSL.